This invention relates to protection apparatus for liquid-filled submergible equipment, such as electric motors, which may be used, for example, in oil and other wells for driving downhole pumps.
It is desirable to protect submergible motors and the like against the ingress of possibly harmful fluids in which the motors may be immersed, for example corrosive well fluids. Accordingly, it is common practice to fill such motors with a benign liquid, such as a suitable lubricating oil, and to use a motor protector to isolate the motor interior from its surrounding environment and accommodate changes in volume of the motor liquid, which might otherwise lead to external fluid being drawn into the motor.
Different types of protectors have previously been used with downhole submergible motor-pump assemblies. A first type, for example, has open communication with the external well fluid and utilizes a labyrinth path, which takes advantage of the natural gravity separation between the well fluid and the internal motor liquid, to minimize mixing of these. A second known protector is of the positive seal type, which uses a flexible diaphragm, bellows, or other pressure communicating barrier system to provide an interface between the motor liquid and the well fluid. A third known type of protector is similar to the first type, but has a chamber filled with an inert barrier fluid having a higher specific gravity than both the well fluid and the motor liquid. This type of protector relies on the high specific gravity of the inert fluid to prohibit interchange between the well fluid and the motor liquid. Examples of known motor protectors may be found in U.S. Pat. Nos. 2,674,702; 2,783,400; and 2,854,595.
While known protectors have proven to be servicable and reliable for most submergible motor applications, they have certain weaknesses, generally arising from harsh well environments, to which the known devices are not well suited. Also, when a well's direction deviates from the vertical, gravity separation of the well fluid and motor liquid is less effective, and may be greatly diminished for deviations greater than 45 degrees. Positive seal protectors inherently create a pressure differential between the well fluid and the motor liquid. This pressure differential, if negative (for example, motor liquid at a lower static pressure than the well fluid) can lead to contamination of the internal system due to leaks at locations such as joints, cable entry ports, shaft seals and the like.
Additionally, prior protectors provide no means for enunciating a state of potential contamination failure, or other deleterious effects before such effects produce undesirable consequences in the protected equipment.